Electrolytic capacitor and method of making



Oct. 10, 1967 J. A. MORESI, JR., ETAL 3,3

ELECTROLYTIC CAPACITOR AND METHOD OF MAKING Filed April 16, 1964 IINVENTORS JbSe hAJfO resi,Jn Alberifiickernfl fiw ATTORNEYS UnitedStates Patent 3,346,781 ELECTROLYTIC CAPACITOR AND METHOD OF MAKINGJoseph A. Moresi, .113, North Adams, and Albert E. Scherr I11,Wiiliarnstown, Mass., assignors to Sprague Electric Company, NorthAdams, Mass, a corporation of Massachusetts Filed Apr. 16, 1964, Ser.No. 350,350 Claims. (Cl. 317-230) ABSTRACT OF THE DISCLGSURE An extendedfoil electrode electrolytic capacitor with compressed turn ends joinedby metal coatings over only a part of each end having as a workingelectrolyte an electrolyte introduced into the wound section toinitially form the foil electrodes and the method of producing thecapacitor.

This invention relates to low voltage electrolytic capacitors of highcapacitance of the type used in computers. In particular this inventionrelates to aluminum electrolytic capacitors having a case size of aroundtwo to three inches diameter, and the method of assembling thesecapacitors.

Physically large aluminum electrolytic capacitors of low voltage andhigh capacitance are used particularly for transistorized computer powersupply applications. It is important that these units which are to beoperated at about six volts or less have a high reliability at highcapacitance ratings as well as good life characteristics. Of particularimportance are such characteristics as the equivalent series resistance(ESR) which is the sum of the resistances of the oxide dielectric, theelectrolyte-spacer combination, and the foils and tabs; theself-inductance of the turns of the convolutely wound foils; and, changein impedance over a wide range of frequencies.

An object of this invention is to provide an electrolytic capacitor thatis superior to the prior art in lower equivalent series resistance,lower inductance, and lower impedance.

It is another object of this invention to provide a novel aluminumelectrolytic capacitor having superior characteristics and which isproduced by a simplified process.

Another object of this invention is a novel method for forming(producing a dielectric oxide) the capacitor electrodes either anode oranode and cathode by a simplified process.

A further object of this invention is to provide a novel termination ofthe anode and cathode foils of an aluminum electrolytic capacitor to thecapacitor terminals.

These and other objects of this invention will become more apparent uponconsideration of the following description taken together with theaccompanying drawings in which:

FIGURE 1 is a perspective view of a capacitance section according tothis invention on a horizontal axis, and with the section partiallyunwound;

FIGURE 2 is an axial section view of the capacitor section showing thepreferred termination of this invention; and,

FIGURE 3 is an axial section of the preferred encasement of thecapacitor section of FIGURE 2.

The convolutely wound capacitor section of anode and cathode foils andinterspersed paper spacers is assembled by rolling in a conventionalmanner. The anode and cathode foils are of such a width that the windingof the section extends an edge of each foil beyond the lateral edges ofthe porous spacer material. One of the foils is extended at each of thetwo ends of the section so that the resultant section has one of thefoils extending at each of the respective ends.

The termination of the anode and cathode foils to the capacitorterminals is attained by burying the respective anode and cathode foilextensions in a sprayed-on conductive material which simultaneouslyshorts the extended turns and secures the terminal to the turns, andconsequently to the capacitance section. The conductive material isapplied through a mask so that only a portion of the ends of the turnsof foil are covered by the conductive material, thereby leaving theremainder of the end of the section uncovered and open.

The foils are then formed by impregnating the section with a suitableforming electrolyte through the open ends of the section. The previouslyunformed electrode foils are then subjected to a forming voltage toproduce on the surfaces of the electrode foils a dielectric oxide. Theforming takes place after the assembly of the convolutely wound sectionand the attachment of the terminations, and is conducted at a voltagegreater than the desired rated voltage of the capacitor.

As shown in the drawings, capacitor section 10 of FIG- URES 1 and 2 is aconvolutely wound assembly of foil elements 11 and 12 and spacerelements 13. The capacitor section 10 is made up of convoluted layers ofthe pair of foil electrodes 11 and 12 between which are interposed theporous spacers 13 which are preferably composed of paper. In theconvolutely wound section 10 the electrodes are wound on each other inextended-foil fashion with foil 12 extending from the left end of thesection as seen in FIGURE 1 and the foil 11 extending from the rightend, each forming a number of concentric turns of foil. Each of theoverlapping concentric turns of foil is separated from adjacent turns bythe paper spacers 13. There are two paper spacers 13, each separating apair of sides of the foils 11 and 12.

The wound capacitance section 10 is shown with the axis extendinghorizontally in FIGURE 1. Thus, the width of the component parts isalong this horizontal axial dimension. It is seen that one edge ofelectrodes 11 and 12 extends beyond the paper spacers 13 at therespective sides of the section 10. An out edge A of foil electrode 11forms the outer edge of the turns of the right end as seen in FIGURE 1and an out edge B of foil electrode 12 forms the outer edge of the turnsof the left end. The in edge C of the foil 11 is inside the section 10,as is the in edge D of the foil 12.

FIGURE 2 is a section showing the wound layers of electrodes and spacerswith the outedges A and B extending beyond the paper spacers 13 at therespective ends of the section 10. The edges A and B are each compressedso that the convolutions of the respective electrodes 11 and 12 are incontact. These edges A and B are then partially covered by a conductivematerial 14 and 16 respectively, preferably the same material and purityas the foils, as by a metal spray applied through a mask, so as toprovide a common conductor at each of the respective ends of section 10.

In FIGURE 2 the foil electrode 11 is shoWn with the edge A having aconductive material 14 directly interconnecting the turns. A metallicstud 15 encased in resin plug 21 is attached to the conductive strip 14.FIGURE 2 also shows conductive material 16 interconnecting the turns ofelectrode 12, with a metallic stud 17 22 embedded in capacitor.

It will be understood that access to the interleaved layers of foilremains open even after the application of the conductive members 14, 16and studs 15, 17. Although section 10 is tightly wound and compact thenature of porous spacers 13 permits ready penetration of the inencasedin resin plug the material 16 for termination of the terior of thesection by the capacitor electrolyte. Thus, the electrolyte can beintroduced along the surfaces of the foil electrodes 11 and 12 andspacers 13 to completely wet the foil surfaces. A feature of thisinvention is the use of the formation electrolyte as the actual Workingelec- "num electrolytic capacitors. It will be understood that the purealuminum surface of the unformed foils provides a superior surface forthe attachment of the conductive aluminum strips 14 and 16. The goodelectrical and mechanical junction required for noise-free operation atlow voltages is attained in this way.

It is necessary, however, to have a dielectric film on the aluminumelectrode surfaces for the section to function as an electrolyticcapacitor. This is formed by the anodization of the aluminum with asuitable electrolyte, preferably the glycol-borate or glycol-formateelectrolyte known to the art as advantageous working electrolytes forlow voltage aluminum electrolytic capacitors. The elec- V trolyte isimpregnated into the section which is then placed under a formingvoltage which is roughly twice the rated voltage of the capacitor. Thisimpregnation and forming step follows the step of applying theconductive strips 14, 16 and the studs 15, 17. This forming isparticularly effective in producing an aluminum. oxide dielectric whichwill be satisfactory for the voltages in the six volts or less rangenormally demanded of low voltage aluminum electrolytic capacitorsemployed in computer power supplies. It will be understood that whilethe structure of this invention is operable over a wide voltage range,the synergistic combination of structure and in situ formation is bestexperienced in the aforementioned six volts or less range whereincomplete formation of a stable dielectric oxide is assured.

This invention is particularly advantageous in providing a low voltagealuminum electrolytic capacitor With the aforementioned superiorelectrical characteristics. The aluminum electrolytic capacitor of thisinvention has lower equivalent series resistance, lower inductance, andlower impedance changes over a wider range of frequencies thanpreviously known low voltage-high capacitance aluminum electrolyticcapacitors.

The above-described embodiment has illustrated the shorting of the turnsand the application of the conductive strips by spraying with moltenconductive materials such as aluminum. For example, the strip maybe'attached by brazing, welding, or soldering, or by a conductive resin.Known cold welding techniques may also be used. These techniques forshorting the turns and attaching the leads all are so adapted as toleave a substantial portion of the ends of the section open forimpregnation with the electrolyte.

The electrolytic capacitor is preferably completed in the manner shownin FIGURE 3 as by inserting the formed section into a tubular metallichousing 20 and then sealing the housing around plugs 21 and 22 bymetal-working procedures known to the art. Crimps 23 and 24 are producedto provide seats against which the rolling of rim of housing 20 ontoresilientrings 25 and 26 is accomplished. The formation electrolyteremaining within the section is all the electrolyte that is necessaryfor the operation of the capacitor at rated voltage.

While the above-described embodiment illustrates a capacitor designemploying axial leads this invention is not limited to such aconstruction but is equally applicatively being bentover andinterconnected into a common terminal for the respective electrode, eachof said bent over edges extending from the convolute edges of theopposite ends of the section, a first conductive metal coating coveringsubstantially the entire bent over edges of a first of said electrodesand having passages for permitting flow of electrolyte between said bentover edges into and out of said section, and an electrical terminalconnected to said coating, a second conductive metal coating coveringsubstantially the entire bent over edges of a second of said electrodesand having passages for permitting flow of electrolyte between said bentover edges into and out-of said section, and an electrical terminalconnected to said coating, the extended bent over foil edges beinginterconnected at the respective ends by the respective first and secondmetal coatings, each of said bent over edges,'coatings and terminalsproviding through passageways into the convolute layers of said sectionfor circulation of electrolyte and an electrolyte impregnating saidsection, an in situ formed dielectric aluminum oxide on at least one ofsaid electrodes, said electrolyte being retained within said section.

2. The method of producing an electrolytic capacitor comprising windingunformed aluminum electrodes and interleaved porous spacers into aconvolutely Wound capacitor section with a porous spacer adjacent to theelectrode in the section and extending an edge of said electrode fromone end of said section, bending the convolutions at each end of therespective extended edge over the end of the section while providingpassages therebetween, covering substantially the entire bent over edgeswith a conductive metal coating and forming passages therebetween forflow of electrolyte into and out of said section, attaching a conductiveelectrical terminal to the metal coating and impregnating an electrolyteinto said section between the bent over edges and through the passagesin said metal coating, electrolytically forming at least one of thealuminum electrodes with the impregnated electrolyte, and placing thesection in a container.

3. The method of claim 2 wherein the conductive metal coating is sprayedon a portion of the compressed eonvolutions.

4. The method of claim 2 wherein the aluminum electrode iselectrolytically formed during and simultaneously with the circulationof electrolyte into the windings through the terminals. 7

5. In the method of claim 2 sealing the container and retaining theelectrolyte in the section as a working electrolyte.

References Cited UNITED STATES PATENTS 2,094,048 9/1937 Siegel 3172302,290,163 7/1942 Brennan 317-230 2,493,231 1/1950 DeLange 317-2603,100,857 8/1963 Rice et al. 3172.60 3,143,692 8/1964 Terry 3l72603,174,085 3/1965 Schroeder et a1. 3l7230 3,256,472 6/ 1966 Centurioni 3l7260 JAME L KALLAMZ Pr y Examiner- UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,346,781 October 10, 1967 JosephA. Moresi, Jr., et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 4, line 1, after "leads" insert extend line 9 for "spaces" readspacers Signed and sealed this 29th day of October 1968.

(SEAL) Attest:

EDWARD J. BRENNEI Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. AN ELECTROLYTIC CAPACITOR COMPRISING A CONVOLUTELY WOUND CAPACITORSECTION HAVING A PAIR OF ALUMINUM FOIL ELECTRODES SEPARATED BY POROUSSPACES, EACH OF SAID ELECTRODES HAVING CONVOLUTED EDGES EXTENDING FROMONE RESPECTIVE END OF SAID SECTION, EACH OF SAID EDGES RESPECTIVELYBEING BENT OVER AND INTERCONNECTED INTO A COMMON TERMINAL FOR THERESPECTIVE ELECTRODE, EACH OF SAID BENT OVER EDGES EXTENDING FROM THECONVOLUTE EDGES OF THE OPPOSITE ENDS OF THE SECTION, A FIRST CONDUCTIVEMETAL COATING COVERING SUBSTANTIALLY THE ENTIRE BENT OVER EDGES OF AFIRST OF SAID ELECTRODES AND HAVING PASSAGES FOR PERMITTING FLOW OFELECTROLYTE BETWEEN SAID BENT OVER EDGES INTO AND OUT OF SAID SECTION,AND AN ELECTRICAL TERMINAL CONNECTED TO SAID COATING, A SECONDCONDUCTIVE METAL COATING COVERING SUBSTANTIALLY THE ENTIRE BENT OVEREGES OF A SECOND OF SAID ELECTRODES AND HAVING PASSAGES FOR PERMITTINGFLOW OF ELECTROLYTE BETWEEN SAID BENT OVER EDGES INTO AND OUT OF SAIDSECTION, AND AN ELECTRICAL TERMINAL CONNECTED TO SAID COATING, THEEXTENDED BENT OVER FOIL EDGES BEING INTERCONNECTED AT THE RESPECTIVEENDS BY THE RESPECTIVE FIRST AND SECOND METAL COATINGS, EACH OF SAIDBENT OVER EDGES, COATINGS AND TERMINALS PROVIDING THROUGH PASSAGEWAYSINTO THE CONVOLUTE LAYERS OF SAID SECTION FOR CIRCULATION OF ELECTROLYTEAND AN ELECTROLYTE IMPREGNATING SAID SECTION, AN IN SITU FORMEDDIELECTRIC ALUMINUM OXIDE ON AT LEAST ONE OF SAID ELECTRODES, SAIDELECTROLYTE BEING RETAINED WITHIN SAID SECTION.